EPR study ofFe3+inα-quartz: A reexamination of the lithium-compensated center

X-band electron paramagnetic resonance (at ca. 20 K) and lithium-7 electron-nuclear double resonance (at ca. 4 K) studies of a lithium-compensated ${\mathrm{Fe}}^{3+}$ (S=(5/2) center in synthetic iron-doped α-quartz have been carried out. The spin-Hamiltonian parameters were determined, allowing aniso- tropy of the g factor, as well as [g,D,A${(}^7$Li),P${(}^7$Li)]-matrix noncoaxiality, and including high-spin terms of the form $S^4$. The data analysis confirms the model of the center (called $S_1$ by some workers) in which the ${\mathrm{Fe}}^{3+}$ ion occurs substitutionally at a ${\mathrm{Si}}^{4+}$ site, with charge compensation provided by an interstitial lithium +1 ion lying nearby on the same crystal twofold axis. The designation [${\mathrm{FeO}}_4$/Li${]}^0$ is proposed for the center.